Question

Debra earns $7.50 an hour, plus tips, as a waitress. Suppose she works 24 hours in one week. How much money must she receive in tips to earm more than $250 that week?.

Answer 1

The total amount of money Debra earns is the sum of her wage and the tip. Since she earns $7.50 per hour and she worked for 24 hours, her weekly wage is 180. Suppose we let x be the amount of tip, her total earnings is 180 + x. This amount should be more than $250. 
                                       180 + x > 250
                                             x > 70
Thus, Debra should receive more than $70 tip. 

Answer 2

Let x = Debra's earnings in a week; y = tips as waitress

x+y > 250
24*7.50 + y > 250
180 + y > 250
y > 70.

She needs to receive tips more than 70 dollars to earn more than 250 dollars that week.